By the violent competition of electronic information industry, many electronic products raise the operating and processing speed to get the favor of consumers. However, when the operating speed of the chip in the electronic products becomes faster, the operating frequency thereof also becomes faster accordingly such that the working voltage thereof must become smaller. This way, it is caused that the sensitivity of changes of the working voltage of the chip becomes bigger accordingly. Namely, the working voltage provided to operate the chip is unstable which is sometimes a main reason causing the system crash. However, sometimes the instability of the working voltage is only an instant. Therefore, it cannot be waited to measure until the system is crash. The stability of the working voltage has to be monitored anytime and recorded such that the factor of the stability of the working voltage can be taken out of the factors of the system crash to be benefit to developers to know the reason of the system crash.
In general, a prior art voltage detecting circuit, referring FIG. 1, is mainly consisted of a comparator 11 and a zener diode 12. A first resistance 13 and a second resistance 14 are connected at a positive input of the comparator 11, and a third resistance 15 and the zener diode 12 are connected to the negative input thereof. The positive end of the zener diode 12 is connected to the other end of the second resistance 14 and grounded. Further, the output of the comparator 11 is concatenated a fourth resistance 16 and a light emitting diode 17. The positive end of the light emitting diode 17 is connected to the other end of the first resistance 13 and the third resistance 15, and also connected to a voltage source to be measured 18. This way, by the bias caused by the combination of the first resistance 13 and the second resistance 14 collocating with the operation of the comparator 11 and the zener diode 12, the user can observe whether the light emitting diode 17 radiates to determine whether the voltage source to be measured 18 has a situation of voltage surge.
While the previous voltage detecting circuit is simple, if it is desired to be integrated into a chip, usually, the light emitting diode 17 has to be set out of the case for users to visualize whether the light emitting diode 17 radiates directly to determine whether a situation of voltage surge happens. However, such a circuit design has to additionally concern the arrangement of circuit lines, and the manufacturing cost is also increased.
Besides, the light emitting diode 17 only radiates at the instant of the voltage surge happening. After the time of the voltage surge happening, the light emitting diode 17 will not radiate no more. Therefore, the user has to look out whether the light emitting diode 17 radiates anytime. If the user does not pay attention to whether the light emitting diode 17 radiates at the time of the voltage surge happening, whether a situation of unstable voltage happens previously cannot be determined. Therefore, the factor of causing the system crash by unstable voltage cannot be eliminated.